Donald J. Trump at a news conference in New York on Monday.

Donald J. Trump likes to preach flexibility on foreign policy. Why tell America’s adversaries too much, he likes to say, especially when the facts on the ground are constantly changing?

While Mr. Trump’s rivals have said that his approach is evidence of a lack of knowledge, Mr. Trump has been outspoken about how he would handle the rise of the Islamic State in Iraq.

“We go in, we knock the hell out of ’em, we take the oil,” Mr. Trump said on Fox News in August.

Elaborating on CNN that same month, he expressed support for taking an aggressive approach and sending in troops.

“I would go in and take the oil, and I’d put troops to protect the oil,” Mr. Trump said. “I would absolutely go, and I’d take the money source away. And believe me, they would start to wither and they would collapse.”

But as Russia has embarked on its own mission within Syria, launching airstrikes that it says are intended to protect the government and diminish the Islamic State, Mr. Trump has shown his passive side. Essentially, he is happy for Russia to handle it.

“Let Russia take care of ISIS,” Mr. Trump, who opposed the 2003 invasion of Iraq, said this week.

There’s one potential problem, though: The Russian airstrikes are believed to be targeting a rebel insurgent coalition opposed to ISIS, instead of the Islamic State itself. American officials fear that in carrying out the attacks, Russia is trying to weaken opponents of Syria’s embattled president, Bashar al-Assad.

In an interview with the Fox Business Network on Thursday, the billionaire developer, who often describes himself as “very militaristic,” reiterated that he was happy to have Russia lead the fight against the Islamic State in Syria, arguing that he had no problem with letting adversaries battle it out there while the United States sat on the sidelines.

Sounding a bit like one of his rivals for the Republican presidential nomination, Senator Rand Paul of Kentucky, who has been critical of American interventionism, Mr. Trump preached a wait-and-see approach.

“I want to rebuild the United States,” he said. “I want to rebuild our country, our roads, our schools, our airports, instead of just pouring money down the drain.”

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http://www.nytimes.com/politics/first-draft/2015/10/01/shifting-on-islamic-state-donald-trump-welcomes-russias-moves-in-syria/